This invention concerns the handling of cutting fluid used in the machining of metal parts to enable the cutting fluid to be filtered and reused.
In a typical installation, the cutting fluid containing chips and other debris is deposited in a trench extending below the machine tools. The flow of cutting fluid is designed to carry the chips, and other debris down the trench to a pit where filtration apparatus cleans the cutting fluid for reuse.
In order to insure that the chips are carried down the trench, a certain flow velocity is necessary, i.e., 7 ft/sec. is a typical minimum flow velocity with iron or steel chips. This requires a fairly steep slope such that the trench becomes quite deep if a long run is involved. Floor trenches are quite costly to construct, particularly if a double lining is required by environmental regulations, as hidden leaks are a problem as they may exist for long periods, allowing the oil containing cutting fluids to pollute the ground water. In addition, concrete lined trenches below grade make plant revisions more costly and difficult since such trenches cannot be relocated.
Flushing jets are sometimes required to be used in the trenches to assist in sweeping the chips and other solid debris down the trench, but such jets are effective only for short distances, require powerful pumps and interrupt the trench bottom contour. Augmenting flushing flows have also been used, in which additional flows are pumped into the trench such as described in U.S. Pat. No. 4,655,940, again requiring pumps and reducing the capacity of the filter apparatus by diverting filtered liquid from reuse.
Above grade cutting fluid collection systems have also been devised, such as described in U.S. Pat. Nos. 5,466,380; 4,325,663; and 5,223,156. These systems rely on pumps to transfer the fluids above grade, and such pumps are costly and subject to failure. Reliability suffers since the system will not function if there is a pump failure, sometimes requiring that a back up pump be provided, further increasing the system cost.
It is the object of the present invention to provide a handling system for cutting fluid and solid debris which eliminates the need for steeply sloping trenches to establish sufficient flow velocity to insure that chips are cleared from the trench.
It is a further object of the invention to provide a collection system which can be installed above or at grade but which does not rely on pumps or flushing jets in a collection trench.
The above recited objects and other objects which will be understood upon a reading of the following specification and claims are achieved by establishing a vacuum assisted flushing of a closed header pipe extending beneath a series of individual sumps, each receiving cutting fluid and chips from a machine tool installation, the fluid flowing by gravity into each sump.
Each sump has a gravity flow connection to the collection pipe.
The drain header pipe has a down leg which extends to a below grade filter tank, the drawing of the downward leg develops a siphon vacuum when a main control valve at the bottom of the leg is opened to initiate flushing of the collection pipe. The height of the down leg is selected to develop a sufficient vacuum to at least achieve the minimum flow velocity in the header pipe to insure movement of all of the solid debris with the flow of cutting fluid.
The cutting fluid from each sump enters the drain header pipe, with a series of air vents allowing the header pipe to be filled with fluid and chips draining from the sumps with the main control valve closed.
Upon filling of the collection pipe, all of the air vents are closed except for a primary air vent at the upstream end. The fluid and chips quickly drain out of the pipe under the vacuum developed by opening of the header pipe down leg valve, developing a flow velocity in the pipe header sufficient to insure that the chips are carried down the length of the header pipe with the cutting fluid into the filtration apparatus.
The height of the down leg is selected to develop a vacuum level able to overcome the head losses due to friction with the full length of the collection pipe and still develop the minimum flow velocity in the collection pipe.
The sumps can continue to drain into the header pipe during a fluid cycle, but any sump drain may be closed off when the fluid level in that sump declines below a certain minimum level to prevent any air from entering the header pipe during the flush cycle to maintain the vacuum acting on the fluid in the header pipe during a flush cycle.
The header pipe may have a stepped diameter, increasing in a downstream direction such that higher flow velocities can be developed at the upstream end with a smaller flush volume, although a constant diameter header pipe can also be used.